There are various outer connections for electronic devices such as bumps, solder balls, bonding wires, probes, gold fingers, leads, etc. However, not all the outer connections are reliable after long hours of operation due to mismatch of the coefficients of thermal expansion (CTE) between the electronic devices and printed circuit boards connected by the outer connections. The capability of stress absorbing or buffering of the outer connections under larger temperature gradients becomes the key factor for ensuring good reliability. Any breakdown between outer connections and printed circuit boards will cause electrically open which leading to signal disconnections, i.e., system failure.
According to Taiwan Patent Publication Number 535,226 submitted by the applicants, entitled “an electronics device with needle electrodes and their fabrication”, an electronic device with needle electrodes is proposed. Each needle electrode has a dielectric supporting layer to increase the stress absorption capability of the electrodes when under stresses and a metal layer on the dielectric supporting layer to conduct electrical signals to a printed circuit board. Please refer to FIG. 1, an electronic device comprises a substrate 110 and a plurality of needle electrodes 120, wherein the substrate 110 can be a chip, a wafer, a printed circuit board, or a ceramic substrate. A plurality of bonding pads 111 are disposed on the surface of the substrate 110. Each of the needle electrodes 120 includes a metal layer 121 and a PI supporting layer 122, where the metal layer 121 is electrically connected to the corresponding bonding pads 111 and is extended to the supporting layer 122 with a concave curvature. The supporting layer 122 is formed on the bottom of the corresponding metal layer 121 to support the metal layer 121. However, when higher density of electrical connections or smaller line widths and pitches are required, the cross talk and electrical-magnetic interferences between needle electrodes 120 will become severe. The needle electrodes cannot be implemented in high speed, high frequency applications.